Window of Opportunity Clinical Trials to Evaluate Novel Therapies for Brain Tumors

Abstract

Despite significant improvement in understanding of molecular underpinnings driving glioblastoma, there is minimal improvement in overall survival of patients. This poor outcome is caused in part by traditional designs of early phase clinical trials, which focus on clinical assessments of drug toxicity and response. Window of opportunity trials overcome this shortcoming by assessing drug-induced on-target molecular alterations in post-treatment human tumor specimens. This article provides an overview of window of opportunity trials, including novel designs for incorporating biologic end points into early stage trials in context of brain tumors, and examples of successfully executed window of opportunity trials for glioblastoma.

Keywords: Biologic end points; Biomarkers; Brain tumors; Clinical trials; Immunotherapy; Molecular markers; Oncology; Window of opportunity.

Figure 1.. Schema comparing Window of Opportunity Trial concept to Traditional Clinical trials.

In window of opportunity trials, following diagnosis, novel therapies are administered prior to tissue acquisition during surgery. Biological assessment is performed on both treated tissue and an untreated or control tissue to determine if the novel therapy modified its intended target within the tumor (Biological endpoint). This assists with determination of the biologically effective dose. Following surgery, the novel therapy can be continued to determine the maximum tolerated dose (MTD). In traditional clinical trials, novel therapies are administered following diagnosis. MTD and clinical response are assessed without knowledge of the target modification within the tumor.

Figure 2.. Preserving tumor architecture for analysis.

Enbloc tumor resection using a subpial approach preserves tissue architecture for downstream biological analysis including hematoxylin and eosin (H&E) stains, immunohistochemistry (IHC) and western blot analysis.

Figure 3.. Strategy for incorporating Window of opportunity trail design into standard early phase clinical trials.

The Window of oppporunity component can be achieved by designing a separate arm as part of the standard trial. Specfically, Arm A represents the standard arm in which patients are treated with the novel therapeutic and standard clinical outcomes are measured. Patients with resectable tumors are enrolled into Arm B, which is design to provide post-treatment specimens for analysis.

Figure 4.. Strategies for dose-escalation during Window of opportunity trials.

In strategy A, both arms are enrolled at each dose cohort, with arm 2 (biological endpoint arm) enrolling after arm 1 (standard treatment arm). An alternative strategy (B), which is more cost efficient, is to enroll successive cohorts in arm 1 (standard arm) until the MTD is reached. Then, once the MTD is determined, patients are enrolled into arm 2 (biological endpoint).

Figure 5.. Pre-clinical models for evaluating Delta-24 RGD prior to Window of Opportunity Clinical trials.

Preclinical animal models are important for developing assays that can be translated to clinical trials. For example, in the development of Delta-24-RGD, human gliomas were grown in pre-clinical mouse model as shown by H&E stains of mouse brains (A). To develop an assay that would prove viral replicaton and that could be transted to the clinic, we reasoned that there would be three zones of viral replication (C) when animals were sacrificed several days after intratumoral injection: a central zone of necrosis (N, where the virus had killed cells), a surrounding zone of cells that stained positively for hexon or E1B protein (V, where the virus was actively replicating in tumor cells) and a third zone of yet-to-be-infected tumor cells (T, where the virus had not reached yet). These zones were demonstrated in mouse tumors based on H&E (D) and after staining for E1A (red staining in E). This assay was used in a Phase I trial of this agent

Figure 6.. Proposed designs for phase I clinical trials of agents for which molecular targets can be tested and Window of opportunity trial assessing the oncolytic virus, Delta-24-RGD.

Window of opportunity trials can take on several designs (A). Optimal design (Design A). A biopsy can be used to determine the baseline value of the target prior to treatment. Patients are then treated with drug, and the effects of the agent on the tumor are determined in a posttreatment surgical specimen. In design B, which avoids pretreatment biopsy, patients are randomized to receive drug or not. Posttreatment tumor reaction allows comparisons to be made between untreated specimen (controls) and treated specimens. In design C, control specimens are obtained from specimens in a tumor bank. Execution and outcome of a window of opportunity trial for Delta-24-RGD oncolytic virus is shown in B-E. (B) MRI with contrast of long term survivor 3.5 years following Delta-24 treatment and surgery. (C) Photomicrographs of sections from en bloc resection specimens taken 14 days after virus injection. (D) Biological response based on quantitative analyses of CD3+, CD4+, and CD8+ cell infiltration in pretreatment (pre; n = 5) and post-treatment (post; n = 10) tumor specimens. The mean values are noted by horizontal bars; although CD3+ changes were not evident, both CD4+ and CD8+ cells increased after treatment, with increases in CD4+ cells reaching statistical significance. (E) Immunohistochemical staining for viral E1A protein (left), which is a marker of viral infection, and for viral hexon protein (right), which is a marker of replication. E1A immunostaining (left) is primarily intranuclear, as would be expected for actively infecting virus. Immunohistochemical staining for CD68+ Macrophages, CD3+ and CD8+ T-cells. ([A] From Lang FF, Gilbert MR, Puduvalli VK, et al. Toward better early-phase brain tumor clinical trials: a reappraisal of current methods and proposals for future strategies. Neuro Oncol. 2002;4(4):274; with permission. [B–E] From Lang FF, Conrad C, Gomez-Manzano C, et al. Phase I study of DNX-2401 (Delta-24-RGD) oncolytic adenovirus: replication and immunotherapeutic effects in recurrent malignant glioma. J Clin Oncol. 2018;36(14):1419–27; with permission.)